Resistor



Dec. 15, 1942.

RESISTOR Filed Aug. 4, 1940 SILICON CA RBIDE GRA IN S DIUM slucmvINVENTOR.

ATTORNEY.

Patented Dec. 15, 1942 UNITED STATES'PATENT OFFICE RESISTOR Herman O.Stoelting, Milwaukee, Wis., assignor to Line Material Company,Milwaukee, Win, a

corporation of Delaware Application August 4, 1940, Serial No. 351,308

7 Claims.

This invention pertains to lightning arresters of the type whichcomprises a spark gap in series with a resistor of silicon carbide, orthe like, enclosed within a housing of glass or porcelain.

As is well known, the function of the silicon carbide resistor is toeffect extinction of the arc occurring across the spark gap following asurge discharge-which are, once started by the surge, mightdetrimentally be maintained by' the power current in the absence of someefiective counter provision. f

Failures of lightning arresters of the abovementioned type haveheretofore been quite com-' mon as a result of fiashovers occurringbetween the inner surface of the housing and the mass of silicon carbideresistor material-which phe-,

nomenon frequently destroys the further usefulness of the arrester andmay even cause the housing thereof to rupture. The object of this in-.vention is to prevent such fiashovers and thus avoid consequentimpairment or destruction of the arrester.

Prior to the present invention, lightning arrester resistors have beenmade of comminuted silicon carbide bonded with sodium silicate (waterfglg's's? andconverted to as'oirrstawsy deny: fiation or substantialdehydration; and efforts have been made to prevent fiashover by paintingthe exteriors of such bodies with non-conductive materials such asshellac and, alternatively, by

filling the space between the resistor and interior of the housing withvarious non-conductive compounds as' disclosed, for example, in HillUnited States Patent 2,018,672 and Kellogg United States Patent2,050,334. According to my observations and those of other experts inthe art whom I have consulted, none of the expedients above referred tohave proved highly successful in preventing fiashoversunder conditionsordinarily to be expected; but, I have found through exhaustive tests inthe laboratory, confirmed by practical operating experience, thatfiashovers can definitely and consistently be prevented by firmlybonding the resistor element to the interior of the housing with sodiumsilicate; and by "bonding" I mean effecting an actual adherence of thesodium silicate bonding agent to the housin: wall so that' there remainsno infinitesimal space between the resistor and housing along which afiashover can occur. I

The greatly improved performance of lightning arresters in accordancewith the present invention'is the proximate result of the manufacturingmethod employed which brings about a bond beis chemical astute and notmerely a physical adhesion; and this successful method consists inintroducing a wet mixture of silicon bi e and sodium silicate into thehousing and tamping e same wet and plastic into the space it is-lntendedto occupy, in intimate contact with the housing, and then dehydrating orsubstantially dehydrating the mass by which method brings about anattachment between the resistor and housing which is inseparable exceptby dissolving the sodium silicate bonding agent.

' The invention will now be described in detail with reference to .theaccompanying drawing. 1 In the drawing: I

Fig. 1 is an elevational view, partly in section, showing an improvedlightning arrester.

Fig. 2 is a longitudinal sectional view of a housing illustrating themanner in which the mass 2 of resistor'material and sodium silicatebinder is put in place.

. Pig. 3' is a greatly enlarged fragmentary view showing the bondedrelationship of the valve'ma- 'terial andthe housing. 4

Like parts are designated by the same refer.

ence numerals throughout the several views.

Fig. 1 shows a lightning arrester including a tubular cylindricalhousing I, made of porcelain, glass, or other suitable insulatingmaterial and having a bore 2 extending longitudinally throughout thelength thereof.

Numeral 0 indicates the resistor element which comprises a mass ofcomminuted silicon carbide or other suitable material having an averagegrain size of the order of mesh and held together as a solid mass by abinder 4 of sodium silicate-see Fig. 3.

It is sometimes found desirable to add to the sodium silicate binder asmall amount of reduc--.

4o ing agentsuch as potassium permanganate to prevent excessive evo u on0 hydrogen gas which might otherwise interfere with proper bonding ofthe comminuted silicon carbide. A water repellent, such as zinc oxide orcla may also be added to the mixture car e and water Be*fbre the housingI is packed with the mixture of valve material and water glass, thehousing is mounted on a cylindrical plug 6 extending a predetermineddistance into the bore 2 of the housing I. The plug is supported in anysuitable manner at 0.

A predetermined amount of the prepared valve material is packed into thehousing I against tween the resistor and housing which apparently theplug I, by any suitable tamplng device, not

shown, within a predetermined distance from the upper end of thehousing.

After the mixture is packed in the housing, the latter is removed fromthe plug and placed in anoven for drying-substantially all of themoisture of the water glass being thus removed. Fig. 3 showsapproximately the bonding relationshlp of the silicon carbide grains 1with respect to each other and with respect to the housing'l aftercompletion of the drying operation.

It may be noted that each silicon carbide grain is firmly held within afilm or layer of sodium silicate as indicated at l, and point contact ismade at places between the grains as shown at l. I

It is observed that each of the grains is united or bonded by the sodiumsilicate to the adjacent grains as indicated at 0, thereby forming ahomogeneous mass.

It is still further shown that the homogeneous mass of valve material isbonded by the sodium silicate to the housing i as shown at II.

By providing a predetermined amount of zinc oxide, clay, or othersuitable material in the bonding agent, the valve material after beingtreated by heating has a water repellent characteristic. This waterrepellent characteristic eliminates the necessity of immediately sealingthe unit after the heating operation. which would otherwisebe necessaryin order to prevent the absorption oi moisture by the resistor element.

It also looks in the resistor element any moisture remaining thereinafter the heating operation. Should the moisture be permitted to escapeaiterthe arrester goes into service, the

various metal parts of the arrester would become damaged by corrosion,thereby interfering with the proper operation of the arrester.

It may also be noted that the resistor elunent is protected frommoisture during service should the sealing portions of the arresterbegin to leak. After the drying operation a thin film of cop-' withthrough the sprayed copper surface II and the terminal plate II.

The upper end of the housing l'is sealed /against moisture bythe cap IImore fully described and shown in the application of Ralph H. Earle,Serial Number'269,066, filed April 21,

1939, for an isolator.

The lower end of the resistor element I is sealed by means of theterminal plate II in con-' tact against the film of copper ll, an anchornut ll mounted in contact with the plate II. a circular rubber gasketIt. and a metal alloy 20. such as tin and lead, poured around the nut I!and within the rubber gasket as shown. After the metal has cooled it isforced outwardly at 2|, against the rubber gasket. by an appropriatewedging tool, not shown, thereby providing a positive sealing againstmoisture.

a gap device 2:, more fully described and shown in the above notedapplication. is' scarred to the nut ll by the screw 28, and a suitablesealing compound 24 is packed around the gap.

device within the lower end of the housing i.

From the foregoing description it is apparent that the objects of'thisinvention have been at- 75 on acts said hole Mace. said methodconsisttained by providing an overvoltage protective device comprising aresistor element united with the housing to form a homogeneous mass,thereby increasing the life usefulness of the device.

I claim:

1. An over-voltage protective device comprising a housing oi glass orporcelain having a bore, and a resistor fitting said bore and firmlybonded thereto by a solid, nomplastic, substantially desiccate,non-conductive binder so as to form a unified structure with saidhousing, said resistor constituting a partition completely obstructingsaid bore and consisting of a solid, sintered, substantially desiccate,non-plastic. homogeneous. compact mass comprised of many discreteportions of valve material intimately bonded together with asubstantially desiccate, non-conductive binder which permeates saidmass, said. valve material being characterized by high impedanceresistor constituting a partition completely obstructing said bore andconsisting of a solid. sintered. substantially desiccate, non-plastic,homogeneous, compact mass comprised of many discrete portions of valvematerial intimately bonded together with a substantially desiccate,nonconductive silicate binder which permeates said mass. said valvematerial being characterised by high impedance when subjected torelatively low voltage and relatively low impedance when subiected torelatively lah voltage.

3. An over-voltage protective device comprising a housing of glass orporcelain having a bore.

and a resistor fitting said bore and firmly bonded.

thereto by a solid, non-plastic, substantially desconstituting apartition completely obstructingsaidboreandconsistingofasolidsinteredsubstantially desiccate."non-plastic, homogeneous,-

compact mass comprised of comminuted silicon ;earbide intimately bondedtogether with a substantially desiccate, non-conductive binder whichpermeates saidv mass.

.4. An over-voltage protective device comprisingahousingoiglassorporcelsinhavingabore, and a resistor fitting said bore andconstituting a partition therein completely obstructing said bore. saidresistor comprising a compact mass of comminuted silicon carbide, thediscrete particles of which are intimately bonded together between aresistor of the class described and a surfacedefining the bore of aglass or porcelain housing for said resistor, which bond issubstantially-proof against fiashover between said bore surface and saidresistor and wherein said re-' sistor comprises a solid. non-plastic,compact massconsistingofmanydiscreteportionsoi'valve material intimatelybonded together by a nonconductive binder which permeates said mass and9,305,077 ing in preparing a wet, pliable, intimate mixture of saidvalve material and said binder, in liquid form, compacting a mass ofsaid mixture in place in said bore so as to eifect an intimate contactbetween the massof said wet mixture and the surface defining said borewhile at the same time shaping said mass into a partition completelyobstructing said bore and thereafter baking said T mass together withsaid housing until said mass is sintered and substantially desiccated.

-6-. The. method of producing an intimate bond between a resistor of theclass described and a surface defining-the bore of a glass or porcelainhousing for said resistonwhich bond is substan-.

tially proof against flashover between said bore surface and saidresistor and wherein said resistor comprises a solid, non-plastic,compact mass of comminuted silicon carbide bonded together with a binderconsisting principally of a silicate which permeates said mass andcontacts said bore surface, said method consisting in preparing a wet,pliable, intimate mixture of comture 'ofcomminuted silicon carbide andliquid resistor comprises a solid, non-plastic, compact mass ofcomminuted silicon carbide'bonded together with a binder consistingprincipally of sodium silicate which permeates said mass and contactssaid bore surface, said method consisting in preparing a'wet, pliable,intimate mixsodium silicate, compacting a mass of said mixture in placein said bore so as to eifect an intimate contact between the mass ofsaid wet mixture and the surface defining said bore while I at the sametime shaping said mass into a parminuted silicon carbide and a liquidsilicate, compacting a mass of said mixture in place in said bore so asto effect an intimate contact between the mass of said wet mixture andthe surface defining said bore while at the same time shaptition'completely obstructing said bore and thereafter baking saidmass-together with said housing until said mass is sintered andsubstantially desiccated.

HERMAN O. STOEL'I'ING.

